1. Field of the Invention
This invention relates to the field of underwater swimming apparatus. More particularly, it relates to swim fins worn on the feet of underwater swimmers and to a unique construction that compensates for the natural pronation of the foot when using fins.
2. Description of the Prior Art
For man to efficiently swim underwater, he has had to develop certain products to make him more fish-like in his movements. Prime among these products are swim fins that are snugly attached to the swimmer's feet and each contain a large blade moveable by one's legs in an undulating motion. To achieve the highest efficiency in using these fins, the blades of the fins are maintained in a plane perpendicular to the direction of the swimmer's forward movement. This is not always possible due to the nature of one's skeletal makeup.
A person's natural anatomical structure of the ankle and foot results in what is known as "supination" or pigeon-toeing. When the swimmer uses the swim fins in a flutter kick, which is the anatomical flexion and extension of the hips, knees and ankles, the supination causes the fins to turn inward resulting in the plane of the fin blade to be turned away from perpendicularity to the direction of the swimmer's path and loss of efficiency of the fins and the swimmer. This matter is further explained in U.S. Pat No. 4,923,419 issued to Kevin I. McCarthy in 1990. His remedy for this supination was to build a swim fin with the foot pocket offset from the center of the fin.
Further study has shown that supination does not occur in a vacuum. It is often coupled with "pronation" which is the opposite of supination and defined as "the eversion and abduction of the foot causing a lowering of the medial edge thereof", see Stedman's Medical Dictionary, 23rd Edition, Williams & Wilkins, 1979, at page 1147. Pronation shows itself as a slight but noticeable rotation of the foot to the outside when wearing footwear. While it occurs with shoes of all type, namely the tendency to walk on the outside of the shoe, it is most noticeable in wearing swim fins where the foot turns or rotates to the "outside" causing the swim fin to rotate to the outside and out of perpendicularity with the path of travel of the swimmer.
Pronation reduces swim efficiency just as supination does even though they are opposite in feature. In the same Medical Dictionary, "supination" is defined as "the opposite of pronation". Accordingly, what is useful in solving supination problems will not be useful in solving pronation problems.
Further, a review of the prior art of swim fins shows some other problems not to have been solved and that still remain today as impediments to the growth of use of these under water apparatuses. For instance, the foot pocket of swim fins do not take into account the potential for loss or gross reduction of blood flow in the frontal area of the foot (the toes) during prolonged use of the fins. Foot pockets are notoriously tight, evidently to aid in holding the fins in a snug fit to the foot. Such tightness causes pain in the area of the toes and can produce problems that last far longer than the wearing of the fins.
In addition, the fin blade has traditionally been a long, wide fin blade squared off at the front edge without any consideration given to the use of the fin by the swimmer prior to entering the water. The fins interfere with free walking to the point that many call for walking backward in an effort to avoid tripping over the extended fin.
Further, most fins are made from tough materials such as hard rubber, hard plastic and hard plastic-rubber blends with smooth exterior finishes in an effort to provide strength in the water when the fins undergo the flutter kick. However, that same smooth, tough construction makes the fins extremely tough to walk with on dry land. And, walking on dry land with fins on is part and parcel of everyday use of swim fins. In most respects, it is the front edge of the blade that catches on the ground and trips up the swimmer. If it doesn't catch on something, the smooth surface on the bottom of the fin allows the fin to slide on dry land and cause the swimmer to fall down.
Still further, for the most part, swim fins are not used as rudders to guide the swimmer through the water or on the surface thereof. However, there appears no reason that they could not be used as such if constructed in the appropriate manner.